cells that require lots of energy eg muscle/liver/sperm will have lots of mitochondria

ATP is produced in a stage called the electron transport chain, via the 'stalked particles' on the cristae of the inner membrane of the mitochondrion, and the Krebs cycle occurs in the matrix of the mitochondria

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Respiration terms/definitions

Catabolism: breaking down large molecules into smaller ones

Anabolism: combining smaller molecules to form larger ones

Both involve enzymes

Metabolic pathway: a series of small, enzyme-controlled reactions (eg respiration)

Phosphorylation: adding phosphate to a molecule (eg making ATP from ADP + Pi)